Oil refineries frequently include many kilometers of pipes that require cleaning, as for example in fired heaters, where oil is heated during the refining process. One well established cleaning technique is to run a pig through the pipes under hydraulic pressure to clean the pipes. Pigs are typically polyurethane or strangulated foam cylinders or balls that are studded with scraping elements. The inventor has been a pioneer in the art of pigging, and has obtained U.S. Pat. No. 6,569,255 for a Pig and method for cleaning tubes, U.S. Pat. No. 6,391,121 for a Pig and method for cleaning tubes, U.S. Pat. No. 6,359,255 for a Pipe inspection device and method, U.S. Pat. No. 6,170,493 for a Method of cleaning a heater, U.S. Pat. No. 5,685,041 for a Pipe pig with abrasive exterior, U.S. Pat. No. 5,379,475 for a Scraper for a Pipe Pig, U.S. Pat. No. 5,358,573 for a Method of cleaning a pipe with a cylindrical pipe pig having pins in the central portion, U.S. Pat. No. 5,318,074 for a Plug for a furnace header, U.S. Pat. No. 5,265,302 for a Pipeline Pig and U.S. Pat. No. 5,150,493 for a Pipeline Pig.
Intelligent pigs that carry sensors are run through pipes, as for example the pipes in fired heaters, to inspect the pipes with the sensors. It is preferred that the intelligent pigs run at a constant speed. However, the intelligent pigs tend to slow down when encountering obstacles in the pipe. This can cause problems for the operator of the intelligent pig.